Article thumbnail

RCP Vibration Studies: An Examination of Lower Motor Bearing Failures and Their Effects on Shaft Integrity

By Robert G. Kershaw

Abstract

Many cases of high vibration and changing vibration in reactor coolant pumps (RCPs) can be traced to one of several types of degradation in the lower motor guide bearing. This paper presents a comparison of the vibrational characteristics for several failure modes. Included in this list are loss of lubricant, bearing overloading, and time-varying shoe clearance. Each of the examples studied is from an actual pump which underwent a lower guide bearing failure. In each case the pump was operated for an extended period following the onset of the failure mechanism. This type of operation raises the question of its effect on the fatigue life of the pump shaft and other components. This paper provides a simple assessment of the extent to which fatigue life is impacted. I. Background I.1 Design Considerations Experience has shown that one of the most common failures in nuclear main coolant pumps involves the lower motor bearing. Typically, the lower guide bearing is an oil-immersed, segmented shoe bearing. Figure 1 shows the arrangement for a typical Westinghouse, or similarly designed, reactor coolant pump. There are several reasons for the frequency of these failures compared to failures in the other bearings. Collectively, the reasons may be summarized in that main coolant pumps are three-bearing machines, wherein the lower guide bearing has the weakest design of the three. Therefore, under conditions such as misalignment where all the bearings have higherthan-normal loads, it is the lower motor bearing that is most likely to fail

Year: 2008
OAI identifier: oai:CiteSeerX.psu:10.1.1.121.1781
Provided by: CiteSeerX
Download PDF:
Sorry, we are unable to provide the full text but you may find it at the following location(s):
  • http://citeseerx.ist.psu.edu/v... (external link)
  • http://www.nrc.gov/reading-rm/... (external link)
  • Suggested articles


    To submit an update or takedown request for this paper, please submit an Update/Correction/Removal Request.